The present invention generally relates to weight stacks in exercise and/or testing machines for providing a resistance to movement by an exerciser typically through the medium of a movement arm. Resistance weight mechanisms of the prior art have included either a weight stack or a free weight system. In free weight systems, one or more weights are directly mounted to a movement arm. In a weight stack, the weights are stacked one above the other and selectively connectible to a weight stack pin which is an elongated rod extending through central holes in each of the weights. Alignment of the weights is achieved through guide rods located on opposite sides of the pin and extending through holes in the weights on opposite sides of the central holes. The weights are selectively connected to the pin by inserting a key through apertures in the plates and in the weight stack pin.
The present invention is concerned with the weight stack type of resistance described above. One development in the prior art relating to weight stacks has eliminated the guide rods by utilizing projections and recesses on the weights for aligning the weights in the weight stack. Such improvements are shown for example in U.S. Pat. No. 3,971,555 issuing Jul. 27, 1976 and U.S. Pat. No. 4,625,959 issuing Dec. 2, 1986. Additionally, an improvement over the weight alignment methods disclosed in the aforementioned patents is disclosed in U.S. Pat. No. 4,834,365 issuing May 30, 1989 to Arthur A. Jones. In this patent, semi-spherical projections are provided on the weights for seating in recesses of the weights.